With the emergence of environmental issues as a serious concern in recent years and with the rapid growth in the installation of renewal power sources such as solar power and aerogenerators, it is believed that this might be an effective approach for realizing a low carbon society and for solving energy resource problems. However, for the present, such renewable electric power sources tend to have large output fluctuations. Thus, from a view point of electric power quality, renewable electric power sources require adjustment means to offset output fluctuations. As such adjustment means, to date, thermal power generators that have high response speeds have been used. Thus, a dilemma may arise in which, as renewable electric power sources are increased, the number of thermal electric power generators that are not environmentally friendly need to be increased as adjustment means that adjusts large output fluctuations of the renewable electric power sources. Thus, a major issue that arises is the need to provide strong adjustment means that can replace thermal electric power generators. As such adjustment means, it may be effective to use large capacity rechargeable batteries (NaS batteries or the like). However, they might have very high barriers to introduction and operation costs of large capacity rechargeable batteries.
Thus, V2G (Vehicle-to-Grid) technologies have been studied in which combinations between many rechargeable batteries in automobiles that run on electricity and chargers connected to the rechargeable batteries are used as a virtual large capacity rechargeable battery for stabilizing an electric power system, and the automobiles that run on electricity as well as renewable electric power sources would rapidly become common (these automobiles including hybrid type electric vehicles that are provided with a rechargeable battery and with another power source are referred to as EVs (Electric Vehicles)). Propositions for V2G itself have been made from the 1980s. Studies for estimation of macroscopic stabilization effects of the entire electric power network have been successively reported. In addition, for several past years, microscopic control techniques that build practical systems, namely technologies that individually control charging and discharging of many EVs in real time have been studied.
For example, Non-Patent Literature 1 describes a charging/discharging control technique that sets up EVs' drive model, electric power distribution network model, and electric power price's time change model so as to perform optimal scheduling based on particle swarm optimization (PSO) inspired by motions of a shoal of fish.
On the other hand, Patent Literature 1 describes the structure of an EV charging scheduling device and also an optimal charging scheduling based on a genetic algorithm.
Generally, a system that not only charges EVs, but also discharges electricity from EVs to the electric power distribution network (electric power system side) is referred to as V2G. However, a system that only charges EVs may be referred to as G2V as distinct from V2G. In G2V, since the number of charging/discharging cycles decreases, the load imposed on the rechargeable batteries of EVs will decrease.